Boron containing polyvinyl chloride propellent compositions



May 14, 1968 BURTON ET AL. 3,383,253

BORON CONTAINING POLY'V'INYL CHLORIDE PROPELLENT COMPOSITIONS Filed Oct. 25, 1960 2 Sheets-Sheet l a; BURNING RATE (in/sec) BURNING RATE in/sec) II II Ill BURNING RATE (in/sec) 2 3 4 5 67 89|OO 2 3 4 5 6789IOOO PRESSURE sio) M fluriam Kofieri 6:

AGENT May 14, 1968 BURTON ET AL 3,383,253

BORON CONTAINING POLYVINYL CHLORIDE PROPELLENT COMPOSITIONS 2 Sheets-Sheet :3

Filed Oct. 25, 1960 (9 NO 8, 2|.|% AI A 3%9, l5.l%Al El 7%5, 1.1% Al LOO V lO.55%B NO Al PRESSURE psiu E! 3%8 l5.l% Al PRESSURE ps|n O 4. m 3 o o. o a \E n oON mh m ozimnm O 190541 fii 620w! Mai %mw AGENT United States Patent 3,383,253 BORON CONTAENING POLYVINYL CHLORIDE PROPELLENT COMPOSITIONS Joe M. Burton, Alexandria, and Robert G. Shaver, Burke,

Va., assignors to The Susquehanna Corporation, a corporation of Delaware Filed Oct. 25, 1960, Ser. No. 64,960 12 Claims. (Cl. 149-19) This invention relates to new propellent compositionsv More specifically it relates to polyvinyl chloride propellants having improved ballistic properties.

Composite, solid propellants utilizing plasticized polyvinyl chloride (PVC) as fuel matrix and binder for a solid, inorganic oxidizer have become well known in the propellant art. Performance of the PVC propellants can be increased by incorporating a powdered metal, such as Al, as a solid fuel component, which increases the specific impulse because of its high heat of combustion. Although the burning rate of such propellants is generally good, and the burning rate is generally not excessively sensitive to changes in combustion chamber pressure or propellent temperature, in some applications an even higher burning rate and/or reduced pressure exponent, and/or reduced temperature sensitivity is desirable.

The object of this invention is to provide polyvinyl chloride propellants having increased burning rates and reduced pressure and temperature sensitivity.

Other objects and advantages will become obvious from the following detailed description and the drawings.

In the drawings:

FIGURE 1 comprises graphs showing the effect of boron addition on the burning rate of a PVC propellant at different pressures and ambient temperatures.

FIGURES 2 and 3 are graphs showing the effect on burning rate produced by substitution of boron for varying amounts of powdered Al in PVC propellent formulations.

We have discovered that the addition of boron of very small particle size, namely particles having a maximum weight-average particle size of about 5 microns and preferably a maximum weight-average particle size of about 3 microns, to a propellent composition comprising a plasticized polyvinyl chloride fuel binder and a solid inorganic oxidizer, markedly increases the linear burning rate of the propellant and reduces sensitivity of burning rate both to changes in pressure in the combustion chamber and to differences in ambient temperature of the propellent grain. In some cases, optimum results are obtained with boron having a maximum D,,, of about 1 micron.

Propellants characteristically burn at higher rates as the pressure in the combustion chamber increases, the slope of the curve generally being defined by the pressure exponent n. Propellants having high pressure exponents, e.g. pressure exponents approaching 1, are hazardous because of the large increase in burning rate induced by relatively slight increases in combustion chamber pressure, which, in turn, produces a fu:ther increase in chamber pressure. Propellants of low sensitivity to pressure changes have the advantages of improved performance control and usefulness over a wider range of operating pressures.

Burning rate is also sensitive to differences in the ambient temperature of the propellant, and generally increases with increasing temperature. Since environmental temperatures vary with place and season, this is a factor which can undesirably modify the performance of a solid propellent rocket. Reduced sensitivity of burning rate to propellent temperature can, therefore, often be of considerable importance.

The boron of the requisite small particle size increases the burning rate and reduces pressure and temperature sensitivity of both aluminized and non-aluminized PVC 3,383,253 Patented May 14, 1968 propellants. When employed as a burning rate catalyst in a non-metallized PVC propellant, the boron possesses the additional advantage of increasing specific impulse. In the case of aluminized formulations, the boron can be used either as an additive in small amounts or as a replacement for a portion of the aluminum without adversely affecting the specific impulse of the propellant to any appreciable extent.

The amount of boron added to the PVC propellant is not critical, since amounts as small as 0.2% by weight of the composition will generally effect an increase in burning rate. Addition of about 1% generally produces a marked increase in burning rate. The upper limit is determined by such practical factors as castability of the mix, since the very fine particle size of the boron tends to increase the viscosity of the uncured propellent composition; the extent to which it is desired to employ the boron as a solid fuel component; and the particular ballistic properties required for a given application. In general, the practical upper limit of boron addition is about 15% by weight and preferably about 12%.

The boron-containing PVC propellant can be made in any suitable manner, a preferred method being by the plastisol process in which PVC, in the form of small spherical particles, the solid inorganic oxidizer, the powdered boron, and other solid additives, such as a stabilizer for the PVC, powdered aluminum or other metal fuel, and the like, are dispersed in a high-boiling liquid plasticizer, which dissolves the PVC readily only at elevated temperatures, to form a slurry which is cured by heating the mix to the solution temperature of the PVC in the plasticizer.

Any of the high boiling point, organic liquid plasticizers conventionally employed with PVC in propellent production can be employed, such as the butyl, octyl, glycol and methoxyethyl esters of phthalic, adipic, and sebacic acids, high molecular weight fatty acid esters, such as tetrahydrofurfuryl oleate, and the like.

The ratio of PVC to plasticizer is determined largely by such factors as the desired physical properties of the propellent grain and the amount of insoluble solid additives, such as oxidizer, boron, metal fuel, and the like. In general, the minimum ratio by weight of PVC to plasticizer, for acceptable physical properties, is about 1:2, preferably about 2:3. The amount of plasticized PVC fuel binder in the propellant can also be varied within a relatively wide range, depending on the desired physical and ballistic properties of the cured grain, processing requirements, and the particular additives. In general, the minimum amount of plasticized PVC fuel binder is about 8% by weight, preferably about 10%.

Any suitable, finely divided inorganic oxidizer may be employed such as the inorganic oxidizing salts, e.g. ammonium, sodium or potassium perchlorates and nitrates, and the metal peroxides, e.g. sodium and barium peroxide. The amount of oxidizer must, of course, be present in sufiicient amount to maintain active combustion of the PVC fuel matrix, and varies with such factors as the amount of boron and of solid metal fuel additives, if any, such as aluminum, and particular ballistic requirements. Although there are situations in which the oxidizer can comprise as little as about 30% by weight of the composition, in general, it comprises a major proportion by weight.

Powdered metal fuel components, such as Al, Mg, Be, and Zr, can be included in amounts which are largely determined by the desired propellent performance, the atomic weight of the particular metal, oxidizer requirement for formation of the metal oxide, and the like. In general, the metal fuel component constitutes a minor proportion by weight of the total composition.

Example 1 Solid propellent grains having the following composition were prepared:

A. Ingredient: Parts by weight NH ClO (6900 r.p.m. 2TH grind and 24 mesh, 4:1) 75.00 PVC 11.00 Dibutyl sebacate 12.75

British wetting agent (glyceryl monooleate,

pentaerythritol dioleate, dioctyl sodium sul- Weight-average particle size.

'All of the grains were prepared by mixing the components, pouring the mix into a mold, and heating to about 350 F. to disolve the PVC in the dibutyl sebacate plasticizer.

The burning rate of each of the sample grains was measured in 21 Crawford strand burner at different pressures and at different ambient grain temperatures, as shown in the curves of FIGURE 1. From these experimental data, the sensitivity of the burning rate to changes in combustion chamber pressure and to changes in ambient grain temperature Were determined.

The following table summarizes the ballistic data obtained at a chamber pressure of 1000 psi.

Propellant Temperature 13.11., 11,

F. in./see.

65 0. 365 0. 49 70 0. 46 0. 49 200 0. 57 0. 49 TTkn O.32%/ F.

-65 O. 38 0. 45 70 O. 48 0. 45 0. 575 0. 45 1.- '..0 29%/F. 0. 48 0. 33 70 0. 58 0. 33 O. 69 O. 33

1 Pressure exponent. 2 Temperature eoeilicient of burning rate at constant 1.1,, (nozzle eoeflieient), [an is the ratio of burning surface area to nozzle throat area.

It will be observed that addition of the finely divided boron, to an appreciable extent at the 1% level and very substantially at the 3% level, increases the burning rate, reduces the pressure exponent, and reduces temperature sensitivity.

Example 2 Solid propellent grains having the following composition were prepared:

A. Ingredient: Parts by weight NH CIO (6900 rpm. 2TH and 24 mesh,

In formulations B, C, and D, for each percent of boron added, 1 percent of oxidizer was added and 2 percent of aluminum removed to retain the proper stoichiometry for maximum specific impulse. The atomic weight of Al (26.98) is more than twice that of boron (10.82).

The mixtures were processed, cured, and tested substantially as described in Example 1. Ballistic properties at different combustion chamber pressures are summarized in the graphs of FIGURE 2 and in the following table. All of these tests were made at an ambient propellent temperature of 70 F.

13.11.. in./se':. 1,000 13.5.1.

Example 3 Solid propellent grains having the following composition were prepared:

A. Ingredient: Parts by weight NH ClO (6900 rpm. 2TH and 24 mesh,

The mixtures were processed, cured, and tested substantially as described in Example 1. Ballistic properties at different combustion pressures are summarized in FIG- URE 3 and in the following table. All tests were made at an ambient propellent temperature of 70 F.

13.1%.. n, Propellant inJscc 1,000 p.s.i.

1,000 ps r Although this invention has been described with reference to illustrative embodiments thereof, it will be apparent to those skilled in the art that the principles of this invention can be embodied in other forms but within the scope of the claims.

We claim:

1. In a propellent composition consisting essentially of an organic fuel matrix consisting essentially of polyvinyl chloride plasticized with a high-boiling, organic liquid plasticizer and a finely-divided solid inorganic oxidizer in sufficient amount to maintain active combustion of said organic fuel matrix, the improvement in which said composition includes up to about 15 weight percent of finelydivided boron having a maximum weight-average particle size of about 5 microns, said boron functioning to increase the burning rate of said propellent composition.

2. The propellent composition of claim 1 in which the plasticizer is selected from the group consisting of high boiling liquid esters of phthalic, adipic, and sebacic acids.

3. The propellent composition of claim 1 in which the maximum weight-average particle size of the boron is about 3 microns.

4. The propellent composition of claim 3 in which the maximum weight-average particle size of the boron is about 3 microns.

5. The propellent composition of claim 4 in which the metal fuel is aluminum.

6. The propellent composition of claim 3 in which the oxidizer is ammonium perchlorate.

7. The propellent composition of claim 4 in which the oxidizer is ammonium perchlorate.

8. The propellent composition of claim 5 in which the oxidizer is ammonium perchlorate.

9. The propellent composition of claim 3 in which the plasticizer is selected from the group consisting of high boiling liquid esters of phthalic, adipic, and sebacic acids.

10. The propellent composition of claim 5 in which the plasticizer is selected from the group consisting of high boiling liquid esters of phthalic, adipic, and sebacic acids.

11. In a propellent composition consisting essentially of an organic fuel matrix consisting essentially of polyvinyl chloride plasticized with a high-boiling, organic liquid plasticizer, a finely-divided metal fuel, and a finelydivided solid inorganic oxidizer in suflicient amount to maintain active combustion of said fuel components, the improvement in which said composition includes up to about 15 weight percent of finely-divided boron having a maximum Weight-average particle size of about 5 microns, said boron functioning to increase the burning rate of said propellent composition.

12. The propellent composition of claim 11 in which the metal fuel is aluminum.

References Cited 5 UNITED STATES PATENTS 2,966,403 12/1960 Weil 52-0.5 2,970,898 2/1961 Fox 52-O.5 2,995,431 8/1961 Bice 14919 10 OTHER REFERENCES Zaehringer, Missiles and Rockets, vol. 4, No. 6, Aug. 11, 1958, pp. 28, 29, 31, 32, 34 and 37.

Chem. and Eng. News, July 27, 1959, pp. 22 and 23. 15 Zaehringer, Modern Plastics, vol. 34, October 1956,

pp. 148 to 151.

BENJAMIN R. PADGETT, Primary Examiner.

20 LEON D. ROSDOL, OSCAR R. VERTIZ, Examiners. 

11. IN A PROPELLENT COMPOSITION CONSISTING ESSENTIALLY OF AN ORGANIC FUEL MATRIX CONSISTING ESSENTIALLY OF POLYVINYL CHLORIDE PLASTICIZED WITH A HIGH-BOILING, ORGANIC LIQUID PLASTICIZER, A FINELY-DIVIDED METAL FUEL, AND A FINELYDIVIDED SOLID INORGANIC OXIDIZER IN SUFFICIENT AMOUNT TO MAINTAIN ACTIVE COMBUSTION OF SAID FUEL COMPONENTS, THE IMPROVEMENT IN WHICH SAID COMPOSITION ICLUDES UP TO ABOUT 15 WEIGHT PERCENT OF FINELY-DIVIDED BORON HAVING A MAXIMUM WEIGHT-AVERAGE PARTICLE SIZE OF ABOUT 5 